From the help page from Proboards:
How do I create a board?
On the admin page, click on "Edit Boards (reorder/create/remove)." Scroll down and you will see "Create New Board" near the bottom. Enter an ID for the board (just 1 word describing it, it doesn't matter what you put), the name of the board, a short description, and who the moderators will be. You should separate moderators using commas, and no spaces.
Help page for Proboards is here: http://proboards8.com/help/